5
MAJOR BOAT OPERATIONS AND SYSTEMS
Now that you have some basic terms under your belt, let’s look at some of the basic boat
functions you need to understand and have command of to safely operate your boat.
Trim
Most outboard boat models are equipped with power
tilt and trim mechanisms. The purpose of power tilt
function is to raise the engine for launching, loading
or trailering your boat. The power trim function may
be used to adjust the boat’s planing performance
and running attitude. Trim refers both to the weight
distribution inside the boat and the angle of thrust of
the drive unit. The angle of thrust of the drive unit
forces the bow up or down. The proper trim angle will
vary depending on the load and weight distribution in
your boat. If the drive is trimmed to far in, it will drive
the front of the boat down into the water causing a
condition known as “bow steer” where the outboard
loses its ability to effectively control the direction of
the boat. If trimmed to far in in waves, you run the
risk of driving the bow beneath the water (also known as “stuffing” a boat). Stuffing a boat can
cause harm, damage and could even result in sinking. If the drive is raised too far, you will
cause the propeller to "ventilate" or “cavitate”, resulting in a sudden increase in engine RPM as
well as a loss of speed and control. If this occurs, immediately reduce engine speed and lower
the drive until the condition is corrected. In certain circumstances, improper trim and/or weight
distribution can cause a boat to rotate or “spin out”. Always distribute weight evenly side to side
and mostly to the rear of your boat. Never allow persons to sit in any area other than those
designated specifically for seating. Finally, never exceed the maximum weight printed on the
capacity sticker inside your boat.
Propeller
The propeller converts the engine’s power into thrust to propel the boat. The right propeller for
any boat in a specific application is one that allows the engine to turn up to its full rated RPM,
but no more. It is necessary for the engine to turn to full rated rpm in order to develop full rated
power. If the boat is used for more than one type of activity, fishing and water skiing for
example, the prop can only be optimized for one situation. Since a spare propeller is an
excellent safety item, the purchase of a second propeller which is more efficient for another
application is not all “added expense”. Propellers are identified by two numbers such as 14 x 17,
